Division VI / Commission 34 / Working Group Astrochemistry (original) (raw)
Related papers
Observational astrochemistry: The quest for interstellar molecules
EPJ Web of Conferences, 2011
Over 160 molecular species, not counting isotopologues, have been identified in circumstellar envelopes and interstellar clouds. These species have revealed a wealth of familiar, as much as exotic molecules and in complex organic (and silicon) compounds, that was fully unexpected in view of the harshness of surrounding conditions: vanishingly low densities, extreme temperatures and intense embedding UV radiation. They illustrate the diversity of astrochemistry and show robust prebiotic molecules may be. In this lecture, we review the quest for interstellar molecules and show how tributary it is from theoretical ideas and technology developments. A. A. Penzias, who discovered interstellar CO and the 2.7 K Cosmic Background radiation, used to joke that astronomical research is easy: the great questions have largely been formulated; one only has to wait until technological progress makes it possible to answer. 1. THE FIRST STEPS The presence of diffuse gas between stars became clear some 100 years ago, when it was realized, in the course of spectroscopic studies of bright stars, that some absorption lines were too narrow to come from stellar atmospheres and must arise from a much cooler, low density medium: interstellar (IS) gas. Although most narrow lines were readily identified with electronic transitions of atoms, such as Na, Ca, K and Mg, some, dubbed U-lines, eluded any assignment. It is only in 1937 that P. Swings and L. Rosenfeld tentatively assigned several U-lines between 388 nm and 430 nm to the diatomic radical CH [25]. Shortly later, Andrew McKellar [22] assigned two U-lines in the same wavelength range to a second radical, CN; finally Douglas and Herzberg [8] assigned 3 U-lines to CH + , after succeeding in forming this cation in an electric discharge and measuring accurately its spectrum. Interstellar molecules were born, although not yet interstellar chemistry. It is worth noting that the discovery of the first interstellar molecules was made possible by the conjunction of two major advances: the construction of the 100 inch Hale telescope, which made high resolution spectroscopy possible, and the birth of molecular spectroscopy thanks, in particular, to Gerhard Herzberg (Fig. 1). In the next decades, such lucky conjunctions repetitively acted to enlarge the interstellar molecule zoo. 2. RADIO TAKES OVER Twenty years elapsed before the next major step, which occurred thanks to the development of microwave spectroscopy and radio astronomy. The latter stemmed out of radar development during World War 2, particularly of the work directed by I.I.
The Astrochemical Observatory: Molecules in the Laboratory and in the Cosmos
Journal of the Chinese Chemical Society, 2012
Astrochemistry is a discipline consolidated recently, although its roots extend back to the dawn of early civilization with the observation and mapping of the sky. The way to the understanding of the common natural laws on earth and in space paved by Galilei's observations by the telescope, has been extended in the last decades, by new technologies such as radioastronomy and space missions. Plenty of new chemistry was surprisingly discovered. Extreme rich information on the chemical "composition" of the universe is being obtained, either from the other planets and satellites in the Solar System, from meteorites and comets, or from the interstellar space. In this article we will present selected topics regarding the chemical structures and reactions being discovered. Particular attention will be devoted to aspects considered as relevant for the prebiotic processes on earth, such as those involving chirality and its role played in the origin and evolution of life.
Molecules as Tracers of Galaxy Evolution
EAS Publications Series, 2011
Studying the molecular phase of the interstellar medium in galaxies is fundamental for the understanding of the onset and evolution of star formation and the growth of supermassive black holes. We can use molecules as observational tools exploiting them as tracers of chemical, physical and dynamical conditions. In this short review, key molecules (e.g. HCN, HCO + , HNC, HC 3 N, CN, H 3 O +) in identifying the nature of buried activity and its evolution are discussed including some standard astrochemical scenarios. Furthermore, we can use IR excited molecular emission to probe the very inner regions of luminous infrared galaxies (LIRGs) allowing us to get past the optically thick dust barrier of the compact obscured nuclei, e.g. in the dusty LIRG NGC4418. High resolution studies are often necessary to separate effects of excitation and radiative transport from those of chemistry-one example is absorption and effects of stimulated emission in the ULIRG Arp220. Finally, molecular gas in large scale galactic outflows is briefly discussed.
The Next Decade in Astrochemistry: An Integrated Approach
2009
Introduction: The Transformational Role of Astrochemistry: Among the most fundamental questions in astronomy are those concerning the formation of stars and planets from interstellar material and the feedback mechanisms from those stars on the dynamics and chemical evolution of the ISM itself. Studies of the Milky Way and other galaxies in the Local Group have shown that massive molecular clouds are the principal sites of star formation (e.g. Rosolowsky and Blitz 2005). The resultant stars can limit the star formation process as their radiation heats and disperses the remaining cloud (e.g. Matzner 2002). Star formation itself generally proceeds through the formation of a proto-planetary disk, which in turn leads to the establishment of planetary systems (e.g. Glassgold et al. 2004) and the creation of reservoirs of icy bodies. Such reservoirs are the sources of comets, asteroids, and meteorites, which provide a continuing source of material to planets via bombardment (e.g. Mumma et al. 2003). The material in stars is subject to nuclear processing, and some of it is returned to the ISM via supernovae and mass loss from other evolved stars (Asymptotic Giant Branch (AGB), red giants and supergiants: e.g. Wilson 2000). In our galaxy, planetary nebulae, which form from AGB stars, are thought to supply almost an order of magnitude more mass to the ISM than supernovae (e.g. Osterbrock 1989), although the relative contributions depend on the star formation rate (SFR) and the Initial Mass Function (IMF). These processes, along with possible accretion of material from outside the galaxy, replenish the ISM and lead to the formation first of diffuse interstellar clouds with modified composition and then of dense clouds in which stars can again form. A graphic illustrating the life cycle of interstellar material and its connection to planets, including Earth, is shown in Figure 1. Radio, millimeter and sub-millimeter molecular line observations provide crucial insights into almost all phases of the ISM, from overall galactic evolution to the composition of planetary atmospheres and hence the possible development of life forms on Earth-like planets. Molecules Figure 1: The life cycle of the interstellar medium and its relationship to planets and solar systems, as traced by molecular material.
Research in Astronomy and Astrophysics, 2012
One of the stumbling blocks for studying the evolution of interstellar molecules is the lack of adequate knowledge of the rate coefficients of various reactions which take place in the Interstellar medium and molecular clouds. Some of the theoretical models of rate coefficients do exist in the literature for computing abundances of the complex prebiotic molecules. So far these have been used to study the abundances of these molecules in space. However, in order to obtain more accurate final compositions in these media, we find out the rate coefficients for the formation of some of the most important interstellar pre-biotic molecules by using quantum chemical theory. We use these rates inside our hydro-chemical model to find out the chemical evolution and the final abundances of the pre-biotic species during the collapsing phase of a proto-star. We find that a significant amount of various pre-biotic molecules could be produced during the collapsing phase of a proto-star. We study extensively the formation these molecules via successive neutralneutral and radical-radical/radical-molecular reactions. We present the time evolution of the chemical species with an emphasis on how the production of these molecules varies with the depth of a cloud. We compare the formation of adenine in the interstellar space using our rate-coefficients and using those obtained from the existing theoretical models. Formation routes of the pre-biotic molecules are found to be highly dependent on the abundances of the reactive species and the rate coefficients involved in the reactions. Presence of grains strongly affect the abundances of the gas phase species. We also carry out a comparative study between different pathways available for the synthesis of adenine, alanine, glycine and other molecules considered in our network. Despite the huge abundances of the neutral reactive species, production of adenine is found to be highly dominated by the radical-radical/radical-molecular reaction pathways. If all the reactions considered here are contributing for the production of alanine and glycine, then neutralneutral & radical-radical/radical-molecular pathways both are found to have significant contribution for the production of alanine, whereas radical-radical/radical-molecular pathways plays a major role in case of glycine production.
Infrared Observations and Interstellar Molecules
Highlights of Astronomy
It has been common practice to separate the study of interstellar matter from that of stellar evolution. However, infrared astronomy deals mainly with observations of stars forming and stars dying. Interstellar matter represents a phase intermediate between these two stages, part of a cyclic process (Figure 1).We find molecules in interstellar space and want to know how they came to be there. Molecules form most easily at high densities and moderately high temperatures. These conditions prevail both in envelopes around forming stars and also around evolved red giants. However, the matter going into star formation is mainly leaving interstellar space, while that from the red giants is going into space. Therefore the evolved red giants are potentially the source of interstellar molecules.This paper will propose first that the chief interstellar solid molecules were formed in the atmospheres of red giant stars. Volatile solids that might condense in space do not seem to be a major cons...
Molecules in the early universe
The Astrophysical Journal, 1984
We study the formation of first molecules, negative Hydrogen ions and molecular ions in model of the Universe with cosmological constant and cold dark matter. The cosmological recombination is described in the framework of modified model of the effective 3-level atom, while the kinetics of chemical reactions in the framework of the minimal model for Hydrogen, Deuterium and Helium. It is found that the uncertainties of molecular abundances caused by the inaccuracies of computation of cosmological recombination are about 2-3%. The uncertainties of values of cosmological parameters affect the abundances of molecules, negative Hydrogen ions and molecular ions at the level of up to 2%. In the absence of cosmological reionization at redshift z = 10 the ratios of abundances to the Hydrogen one are 3.08×10 −13 for H − , 2.37×10 −6 for H 2 , 1.26×10 −13 for H + 2 , 1.12×10 −9 for HD and 8.54 × 10 −14 for HeH + .
Astrophysical and astrochemical insights into the origin of life
Reports on Progress in Physics, 2002
Stellar nucleosynthesis of heavy elements such as carbon allowed the formation of organic molecules in space, which appear to be widespread in our Galaxy. The physical and chemical conditions-including density, temperature, ultraviolet (UV) radiation and energetic particles-determine reaction pathways and the complexity of organic molecules in different space environments. Dense interstellar clouds are the birth sites of stars of all masses and their planetary systems. During the protostellar collapse, interstellar organic molecules in gaseous and solid phases are integrated into protostellar disks from which planets and smaller solar 0034-4885/02/101427+61$90.00
Organic Compounds in Circumstellar and Interstellar Environments
Origins of life and evolution of the biosphere : the journal of the International Society for the Study of the Origin of Life, 2015
Recent research has discovered that complex organic matter is prevalent throughout the Universe. In the Solar System, it is found in meteorites, comets, interplanetary dust particles, and planetary satellites. Spectroscopic signatures of organics with aromatic/aliphatic structures are also found in stellar ejecta, diffuse interstellar medium, and external galaxies. From space infrared spectroscopic observations, we have found that complex organics can be synthesized in the late stages of stellar evolution. Shortly after the nuclear synthesis of the element carbon, organic gas-phase molecules are formed in the stellar winds, which later condense into solid organic particles. This organic synthesis occurs over very short time scales of about a thousand years. In order to determine the chemical structures of these stellar organics, comparisons are made with particles produced in the laboratory. Using the technique of chemical vapor deposition, artificial organic particles have been cre...